Field of the Invention
This invention relates generally to motors and, more particularly, to an apparatus and method for seating carbon brushes on the commutators of brush-type motors or generators.
It is well known that many motors and generators are in use world-wide and one of the most difficult and tedious tasks is to seat the carbon brushes so that the brushes fit the contour of the commutator. By "seating" we provide a concave arc in the contact surface of the brush complimentary to the convex portion of the periphery of the commutator upon which the brush rides. In the lifetime of a motor, generator or the like, it may be necessary to resurface the brushes at various intervals in order to maintain the efficiency of the machine.
A method of accomplishing this, is to place a carbon brush in its respective brush holder and then place a small piece of sandpaper between the commutator and the brush with the abrasive surface facing the brush. Pressure is then applied to the brush and the sandpaper moved back and forth. This is continued until the brush has achieved substantially the same curvature as the commutator. Of course, this process must be repeated with every brush rendering the process tedious and time consuming.
After all of the brushes have been seated in the above manner, they must be pulled from their respective holders and numbered to insure their proper location. The motor or generator must then be thoroughly cleaned to remove carbon dust and sand from the commutator and its surroundings. The brushes can then be replaced in their proper holders.
Another seating technique first requires the removal of the old brushes and the substitution therefore with new ones. A large abrasive stone is then placed on the commutator while the motor or generator is rotating at maximum speed, and about ten pounds per pressure is applied to the stone moving it from side to side on the commutator. As the abrasive material is worn from the stone, it in turn wears away the surface of the brush. Unfortunately, this process does not assure a good seat and still results in the creation of a substantial amount of carbon dust which must be cleaned from the motor or generator before it can be placed back in production. Furthermore, this approach can significantly reduce the useful life of the commutator.
U.S. Pat. No. 2,725,697 entitled PROCESS FOR SEATING THE BRUSHES OF AN ELECTRIC COMMUTATOR, discloses a seating process comprising the application by brushing, spraying or the like of abrasive particles suspended in a liquid vehicle having a resin or resin forming substance therein to form a peelable coating on the surface of the commutator. After the abrasive coating has dried and hardened, the commutator is rotated with the brushes in contact with the abrasive coating and in this way, the brushes are ground or resurfaced so that the surfaces thereof have the same curvature and contour as the commutator surface. When the brushes have been ground to fit the circular contour of the commutator, the thin plastic film is peeled from the surface of the commutator, bringing the bare surface thereof into contact with the brushes which are now properly seated so as to provide maximum contact between the brush surfaces and the commutator.
U. S. Pat. No. 3,105,331 entitled BRUSH SEATING TECHNIQUE, discloses a method wherein a thin coating of liquid having abrasive particles suspended therein is applied to the surface of a rotating current collector with the surface of the unseated engaging the current collector. The liquid brush seating agent is preferably water having colloidal silica and suspended particles of aluminum oxide dispersed therein. The brush is seated by continuing to rotate the commutator with a surface of the brush in contact therewith. Unfortunately, the methods associated with the above two cited patents require extensive cleaning of the commutator and its surroundings to remove accumulated carbon dust and abrasive particles.